Examples of multilayer coil devices of the above-described type include a multilayer inductor described in Japanese Unexamined Patent Application Publication No. 2005-109097. This multilayer inductor is formed by alternately stacking insulating layers and substantially spiral coil patterns. With the multilayered coil patterns having multiple turns, this multilayer inductor achieves higher inductance.
However, in the multilayer inductor described above, the higher inductance results in a longer coil length, which may lead to increased direct-current resistance.
If the line width of the entire coil patterns is increased to reduce the direct-current resistance, the following problems may arise.
FIG. 4 is an exploded perspective view diagram of a known multilayer coil device 11 having a multilayer body 12 including insulating layers 141-145 alternately stacked with electrically conductive spiral coil patterns 151-154. End portions 151b, 152a, 152b, 153a, 153b, 154a of the coil patters are connected via through holes (not shown) in the insulating layers 152, 153 and 154. Extraction electrodes 161 and 162 are connected to ends of respective coil patterns 151 and 154. External electrodes 13-1 and 13-2 of the multilayer coil device 1 are respectively connected to extraction electrodes 161 and 162. FIG. 5 shows a plan view of a coil pattern 152 on insulating layer 142 of the known multilayer coil device 1 shown in FIG. 4. In a multilayer inductor, such as that illustrated in FIG. 4 and FIG. 5, increasing the line width of coil patterns reduces an inside diameter area S of a coil part and a width of a side gap G. This may reduce an inductance value or cause deterioration of direct-current superimposition characteristics.
Additionally, since the coil patterns are substantially spiral in shape, if, for example, a sheet lamination technique is used as a production method, the coil patterns may be deformed by smearing during screen printing or by pressure applied thereto during stamping. This may cause short circuits between lines of the coil patterns.